Do marine protected areas facilitate coral reef ecosystem health ? An investigation of coral disease and its associated factors in Oahu's marine life conservation districts

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Walton, Maya Maleka
Coral reef ecology; coral disease; marine protected area
thesis / dissertation description
Management actions, such as the use of Marine Protected Areas (MPAs), which enhance fish abundance and diversity, could have important downstream impacts on coral reef ecosystem health and coral reef resilience. Past studies have suggested that protection status not only influences the abundance of fish, macroalgal levels, and coral cover but also the number of diseased coral colonies. Despite the awareness of disease as a coral reef stressor, there has been limited research on the prevalence of disease within Oahu's Marine Life Conservation Districts (MLCDs) which function as no take reserves. Coral reef health in Oahu's three MLCDs compared to three comparable unprotected reefs was investigated. Field surveys were used to quantify coral disease prevalence, coral cover, macroalgal cover, fish abundance and diversity, and coral community size structure at each of the sites. Environmental variables including inorganic-organic carbon fractions of sediments and sediment grain size categories were also measured. Disease assemblages were significantly different between locations and across protection boundaries. Biological and environmental parameters as well as protection status were used in statistical models to determine which variables were the best performing explanatory variables for the prevalence and abundance of five common lesion types in Oahu. Four out of five common lesion types for at least one of the three locations, showed significantly higher levels of prevalence within MLCDs compared to adjacent unprotected areas. Percent cover of the host coral species was the strongest predictor for four out of five models of utilizing disease abundance. Additionally, growth anomalies on Porites lobata were more commonly observed on larger colonies than on smaller colonies. Fish density was significantly higher at the Pupukea MLCD compared to the adjacent unprotected area and coral cover was significantly higher in the Hanauma Bay MLCD and Pupukea MLCD compared to adjacent control sites. Finally while fish density and coral cover were higher in some protected areas compared to control areas, there was no detectable difference in macroalgal cover across protection boundaries for all locations. MLCDs may act as a refuge for fish, but their high coral host abundance may make them vulnerable to more frequent and severe disease outbreaks compared to other locations. Finally while current regulations in MLCDs protect some aspects of coral reef ecosystem health, incorporating strategies aimed at watershed management may further improve MLCD effectiveness and provide more comprehensive protection for coral reefs.